Deck tilt computation system



OR 29921.3;467 Feb. 2, 1960 G. A. CROWTHER 2,923,457

DECK TILT COMPUTATION SYSTEM V Filed Feb. 14, 1956 3 Sheets-Sheet 1 M/ 7/95 Hoe/2007 4 PA A Ni.

//V THE DECK PZA/VE' INVENTOR 550,665 A. (Eon/7W5? ATTORNEY b- 2, 1950 G. A. CROWTHER 2,923,467

" DECK TILT COMPUTATION SYSTEM Filed Feb. 14, 1956 Q 3 Sheets-Sheet 2 INVENTOR v GEORGE A. CEOWTHE Q ATTORNEY 1960 G. A. CROWTHER DECK TILT COMPUTATION SYSTEM 3 Sheets-Sheet 3 Filed Feb. 14, 1956 QQNW m N N R W Km ER wuu mdu \N 1 we mu wmb United States Patent DECK TILT COMPUTATION SYSTEM George A. Crowther, Manhasset, N.Y., assignor to Sperry Rand Corporation, Ford Instrument Company Division, Long Island City, N.Y., a corporation of Delaware Application February 14, 1956, Serial No. 566,067 6 Claims. (Cl. 235-615) The invention relates to the art of naval gunfire control and more particularly to a mcthod and apparatus for determining (1) the relative target bearing Br, i.e., the angle between the vertical plane through a ships centerline and the vertical plane through the line of sight, measured in the horizontal plane clockwise from the bow, and (2) the deck tilt correction jBr, i.e. the change in train due to the inclination of director roller path from horizontal.

In certain types of naval gunfire controls, guns are controlled on the moving ship from a director, which measures the present position of the target in train B'r, i.e., the angle between the vertical plane through the ships centerline and the vertical plane through the line of sight, measured in the deck plane clockwise from the bow, and which measures also the elevation Eb, i.e. the angle between the line of sight and the deck plane measured in the vertical plane through the line of sight. From this data and other data, the predicted position of the target in train and elevation at the end of the time of flight of the projectiles is computed in a computer.

On a ship, director train B'r is measured in the deck plane. Since the ship will roll and pitch, angles measured in the deck plane will vary with this movement and hence must be corrected to compensate therefor. For that reason, it is necessary to convert the data defining the target position which is observed with respect to the deck of the ship to a coordinate system with respect to the earth.

From such data as the director train B'r, the level angle L, i.e., the angle between the deck plane and the horizontal plane measured in the vertical plane through the line of sight, and the cross-level angle Zd, i.e., the angle between the vertical plane through the line of sight and the plane perpendicular to the deck plane through the intersection of the deck plane and the vertical plane through the line of sight, the relative target bearing Br is determined and transmitted to the computer to obtain deflection rates and other fire control quantities. From this data, there is also obtained the deck tilt correction jBr which is transmitted to the gun director to compensate for roll and pitch, so that the director remains sighted on the target, in spite of this ship movement.

The relation of the director train B'r, the relative target bearing Br and the deck tilt correction jBr is jB'r=BrB'r.

In one prior art system, the deck tilt correction jBr has been computed by using variations of the formula cot Br=cot B'r(cos L/ cos Zd) sin L tan Zd and by eliminating Br therefrom, as was done in one case or by eliminating B'r as was done in US. Patent No. 2,658,674.

In these prior art processes and systems, the deck tilt tilt correction jBr has been obtained after obtaining the relative target bearing Br, by subtracting the director and "Ice

train B'r from the relative target bearing Br. The deck correction iB'r so obtained, has been transmitted in the desired form to the director control. However, when so transmitted, the item jBr is subjected to perturbations in both the major angle Br and the angle B'r, especially in rough weather, and therefore, tends to affect adversely the stability of director control.

Also, in certain gunfire controls proposed, the apparatus for obtaining the relative target bearing Br and the deck tilt correction jBr, consisted essentially of potentiometers to obtain a series of trigonometric functions. Such potentiometers being resistance types of devices, they operate through finite steps or resolutions and are subjected to heavy abrasive wear.

One object of the present invention is to provide a new and improved method and apparatus for computing the relative target bearing Br and the deck til-t correction jBr independently, so that perturbations in Br will not aifect jBr.

Another object of the invention is to provide a new and improved method and apparatus, which computes continuously the relative target bearing Br and the deck tilt correction jBr and which consists essentially of a series of electromagnetic basic resolvers and vector solvers of the type affording the advantage of high accuracy due to their infinite resolutions and of long wear due to the absence of abrasive action.

In accordance with certain features of the present invention, the relative target bearing Br is obtained'by solving directly for Br in the equation sin B'r cos Zd cos Br- (cos B'r cos L- sin B'r sin Zd sin L) sin Br=0 this equation representing a true solution of the problem. This involves a solution by servo of a right triangle, the sides of which are sin B'r cos Zd and (cos B'r cos L-sin B'r sin Zd sin L) and whose hypothenuse is the cosine of the angle of pitch N of the vessel. Utilizing the quantities sin B'r cos Zd (cos B'r cos L-sin B'r sin Zd sin L) and the known angle B'r, the sides [(cos B'r cos L-sin B'rZd sin L) sin B'r-sin B'r cos Zd cos B'r] and [(cos B'r cos L-sin B'r sin Zd sin L) cos Br+sin B'r cos Zd sin B'r] of the right triangle containing the angle jBr may be determined. The angle jBr may then be obtained by solving the equation sin jBr: (cos B'r cos L-sin B'r sin Zd sin L) sin B'r-sin B'r cos Zd cos B'r Since the hypothenuse of this angle is the cos N as noted above, the solution will be in error by the percentage cos N differs from unity. Since the pitch of the vessel rarely exceeds 5 and the cosine of an angle so small is close to unity, this error may be ignored. However, by utilizing the customary solution by servo of a right triangle whose sides are known, the angle jBr may be solved with no error.

The formula which is solved for deck tilt correction jBr does not contain the quantity Br, so that any perturbations in this quantity Br does not affect adversely the accuracy of the quantities jBr obtained.

Various other objects, featuresand advantages of the present invention are apparent from (the following description and from the accompanying drawings, in which Fig. '1 is a general diagram of the deck tilt problem solved by the present invention;

Fig. 2 is a diagram including part of the diagram of Fig. 1, showing a phase of the deck tilt problem solved by the present invention;

Fig. 3 is a diagram including part of the diagram of Fig. 1, showing another phase of the deck tilt problem solved by the present invention;

Fig. 4 is a diagram including part of the diagram of Fig. 1 but in a different position and showing still another phase of the deck tilt problem solved by the present invention;

Fig. 5 is a basic circuit of a resolver constituting a component of the systems of Figs. 7 and 8 for mechanizing and solving the derived equations for the relative target bearing Br and the deck tilt correction jB'r;

Fig. 6 is a basic circuit of a vector solver constituting a component of the systems of Figs. 7 and 8 for mechanizing and solving the derived equations for the relative target bearing Br and the deck tilt correction jB'r;

Fig. 7 is a simplified basic circuit diagram for mechanizing and solving the derived equation for the relative target bearing Br and for mechanizing and solving the derived equation for the deck tilt correction iB'r, using a formulation which ignores the departures of the cosine of the pitch angle of the vessel from unity, the full lines in said circuit indicating electrical transmission lines, while the dotted lines indicate mechanical transmission lines; and

Fig. 8 is a simplified basic circuit diagram for mechanizing and solving the derived equation for the deck tilt correction 'B'r, using an accurate true formulation in which the departures of the cosine of the pitch angle of the vessel from unity are considered in the formulation, the full lines in said circuit indicating electrical transmission lines, while the dotted lines indicate mechanical transmission lines.

GLOSSARY A tabulation of symbols and terms involved in the following computations and used in the drawings and in the description in connection with a ship and a gunfire control system thereon is submitted herein.

(B) True Target Bearing. The angle between true north and the vertical plane through the line of sight, measured in a horizontal plane clockwise from true north.

(Br) Relative Target Bearing. The angle between the vertical plane through the ships centerline and the verti cal plane through the line of sight, measured in the horizontal plane clockwise from the bow.

(B'r) Director Train. The angle between the vertical plane through the ship's centerline and the vertical plane through the line of sight, measured in the deck plane clockwise from the bow.

(jBr) Deck Tilt Correction. The change in train due to inclination of director roller path from horizontal (Co) Ship Course. The compass heading of the ship.

(L) Level Angle. The angle between the deck plane and the horizontal plane, measured in the vertical plane through the line of sight, this angle being considered positive when the portion of the deck toward the target is down.

(Zd) Cross-Level Angle. The angle between the vertical plane through the line of sight and the plane perpendicular to the deck plane through the intersection of the deck plane and the vertical plane through the line of sight.

FIRE CONTROL SYSTEM The fire control system, aside from the deck tilt corrector, including the part for computing relative target bearing Br, forms no part of the present invention. A

4 suitable fire control system in which the deck tilt corrector of the present invention may be employed, includes in general a gun director, a stable element and a computer capable of solving gunfire control problems both antiaircraft and surface. The deck tilt corrector of the present invention, constituting part of the computer, receives the director train B'r measured in the deck plane, and receives from the stable element the level L and the cross-level Zd and computes from this data the relative target bearing Br and the deck tilt correction 'B'r independently of said relative target bearing.

The ship course C0 from the fire control gyro compass is combined with the relative target bearing Br in an adding component to form the true target bearing B according to the relationship This true target bearing B, as well as the relative target bearing Br are transmitted to another part of the computer to compute therefrom quantities necessary for proper firing. The ship course C0 drives a generator whose output d(Co), rate of change of Co, is used at the gun director as an aid in tracking. The deck tilt correction jBr derived from the deck tilt corrector of the present invention, drives another generator, whose output is d( 'B'r), the rate of change of jB'r. This quantity d(jBr) is transmitted to the gun director to compensate for the roll and pitch of the ship and to aid thereby in tracking the target.

Derivation of true solution formula for relative target bearing Br and for deck tilt correction jB'r In accordance with present invention, a true solution for the deck tilt problem is employed, except that the cosine of the pitch of the ship is ignored in a specific embodiment, thereby eliminating errors, such as those which would be inherent if an empirical solution were employed. As a result of the present invention, a true solution formula is obtained containing as terms the level angle L, the cross-level angle Zd, the relative target bearing Br and the director train B'r. This formula is solved for the relative target bearing Br by a servo or null seeking system, which so drives the Br line that a balance is obtained between the quantities on opposite sides of the formula.

From the formula indicated, another true solution formula is derived containing the additional quantity jB'r. This additional formula is solved for the deck tilt correction jBr by a servo or null seeking system, separate from that employed in obtaining the quantity Br and operating to so drive the jB'r line that a balance is obtained between the quantities on opposite sides of said additional formula.

The deck tilt problem is indicated in the diagram shown in Fig. 1. This problem is solved in accordance with a true solution, using as inputs the level angle L and the cross-level angle Zd obtained from the stable element on the ship or craft carrying the fire control system, and the director train B'r in the deck plane, obtained from the gun director, to derive the relative target bearing Br in the horizontal plane and the deck tilt correction 'Br.

Considering the right triangle in the deck plane in Fig. 1 containing the angle B'r, the side Y adjacent said angle and the side X opposite said angle, we have X'=sin B'r (1) Y'=c0s B'r (2) Considering the right triangle containing the angle Zd, the side X adjacent to said angle and the side Z" opposite said angle, we have X =X' cos Zd and.

Z"=X' sin Zd X =sin Br cos Zd (3) Z"=sin B'r sin Zd (4) Referring to Fig. 2 showing part of the diagram of Fig. 1, and considering the right triangle in Fig. 2 containing the angle L and the hypothenuse Y', and the right triangle containing the angle L and the hypothenuse Z", we have Y=Y' cos LZ" sin L Substituting from Equations 2 and 4, we have Y=cos Br cos L-sin Br sin Zd sin L (5) tionship ]'B'r=Br-B'r (8) It should be noted from Fig. 1, that the hypothenuse of the right triangle containing the angle Br and the sides X and Y is cos N. Referring to Fig. 4, which is partly derived from Fig. 1, it is seen that d=ef e=Y sin Br f=X cos Br Therefore,

d=Y sin Br-X cos Br (9) Sin jB'r is proportional to or equal to d. Therefore,

sin jB'IEY sin B r-X cos Br From Fig. 4

Y=cos Br cos N X =sin Br cos N Cos N is almost unity within the usual range of pitch, which is rarely above 5. At 2 /2 pitch, the cos N would be .999 and at 5 pitch, the cos N is .996. Therefore, for all practical purposes, cos N can be considered unity and consequently any error resulting therefrom can be ignored. Under these conditions, it can be assumed for approximation, that sin jBr=Y sin B'rX cos Br (10) To determine the exact equation by which the quantity jB'r can be accurately. determined, reference is again made to Fig. 4. It is found therefrom that sin jB 1' Substituting the value of d from Equation 9, there is obtained cos N= Also from Fig. 4

g=Y cos Br and h=X sin Br Therefore,

Y cos Br-l-X sin Br cos cos JB'T From Equations 11 and 12, it is seen that (Y sin Br-X cos Br) cos jB'r-( Y cos Br+X sin Br) sin jBr=0 (13) Equation 13 is the true equation from which the deck tilt correction jB'r may be accurately determined.

Mechanism for solving equations for Br and jB'r The mechanism for solving the equations Br and jB'r is made up of a series of components, which per se, do not constitute the subject-matter of the present invention. The equations to be sloved, however, are such as to lend themselves to eificient solution by well-known components having the characteristics of affording accurate solutions and long life. Some of these components are resolver systems of the electromagnetic type and include two types referred to herein as a basic resolver and a vector solver respectively. A form of basic resolver is shown in Fig. 5 for accommodating one electrical input and one mechanical input. This basic resolver is a motor-like device resembling a two phase, two pole induction motor and consisting essentially of a stator and a rotor, each containing two distributed windings, separated mechanically with respect to each other, the Winding distribution being such that the mutual coupling of rotor and stator would be an exact sinusoid with rotation. The stator windings are indicated as 81-3 and 84-2 and the rotor windings R1-3 and R4-2. With the mechanical rotor input 0 and electrical input E1, the outputs would be Er2=El sin 0 Erl=El cos 0 Fig. 6 shows a vector solver for handling two electrical inputs and one mechanical input. The arrangement of this vector solver is somewhat similar to that of Fig. 5, except that two identical stator windings S'1-3 and S'4-2 are employed to receive two electrical inputs B2 and E1 respectively. The rotor is similar to that of Fig. 5, with two windings R1-3 and R'4-2 displaced mechanically 90 apart. With the mechanical input 0 and electrical inputs E1 and E2, the outputs would be In both of the components of Figs. 5 and 6, a reference input voltage of constant value is applied, although not indicated in the drawings, so that the quantities computed have parametric coefficients. These parametric coefficients are a function of the reference voltage, and for the sake of simplicity will not be indicated hereinafter in the representation of the difierent quantities computed.

Fig. 7 shows a system for mechanizing and solving Equations 8 and 11 to obtain accurate values for the quantity Br and values for the quantity jBr in which the departures of cos N from unity are ignored. In this mechanism, the director train Br from the gun director is fed continuously as a mechanical input into a resolver 10 of the general type shown in Fig. 5, to obtain outputs sin Br and cos Br in the form of voltages. The electrical output sin Br is fed into a resolver 11 of the general type shown in Fig. 5, in conjunction with the mechanical cross-level input Zd obtained from the stable element of the ship, to obtain the two output quantities sin Br sin Zd and sin Br cos Zd=X. The other electrical output cos Br from the resolver 10 and the quantity sin Br sin Zd from the resolver 11 are fed as electrical inputs into a vector solver 12 of the general type shown in Fig. 6, in conjunction with the mechanical input level L derived from the stable element of the ship, to obtain the electrical output cos B'r cos L-sin Br sin Zd sin L=Y The output Y from the resolver 12 and the output X from the resolver 11 are fed as electrical inputs into a vector solver 13 of the general type shown in Fig. 6, in conjunction with the mechanical relative target bearing input Br obtained from a servomechanism 14. The electrical output of the vector solver 13 is X cos Br-Y sin Br which corresponds to Equation 8 and which therefore is equal to zero. If the conditions of the Equation 8 are not satisfied, an error is produced at the output of the vector solver 13, which is a voltage having the proper polarity to drive the servo motor of the servo mechanism to produce a null in the error voltage. When this null is achieved, the quantity Br converted into a mechanical quantity, such as shaft rotation, becomes the relative target bearing Br desired. This quantity Br is transmitted to another part of the computer (not shown) to obtain deflection rates and other fire control quantities.

A servomechanism, such as the servomechanism 14, is well-known per se, and constitutes an automatic drive which positions a mechanical load in accurate correspondence with an input, without placing an appreciable load upon this input. The basic components of the specific servomechanism illustrated in Fig. 7, comprises a servo control 15, a servo amplifier 16, a servo motor 17 and an induction generator 18 connected with a control network, which in the illustrated embodiment is the vector solver 13. Essentially, the vector solver 13 computes a voltage proportional to the error between a function of the input and a function of the output. This error voltage is converted from a high frequency, as for example, a frequency of 400 cycles as a computing reference, to a frequency of 60 cycles by the servo control 15, amplified by the servo amplifier 16 and finally supplied to the servo motor 17 for its control. The servo motor 17 furnishes the mechanical output of the servomechanism, this output being fed back into the vector solver 13 as an input and also driving the induction generator 18. From this generator 18, a voltage proportional to the output velocity is supplied to the servo control 15. This voltage modified and combined with the error voltage from the vector solver 13' in the servo control 15 improves the operation of the servomechanism.

It is seen that the relative target bearing Br is obtained directly from Equation 8, without first obtaining the deck tilt correction fB'r and then adding this correction to the director train B'r.

The deck tilt correction jB'r is obtained independently of the quantity Br by solving Equation 11. For that purpose, the electrical output Y from the vector solver 12 and the electrical output X from the vector solver 11 are fed as inputs into a vector solver 20 of the general type shown in Fig. 6, in conjunction with the mechanical input B'r derived from the gun director, to obtain the electrical output X sin B'r-X cos B'r. The latter quantity is fed into a summing network 21 as an electrical input. This summing network 21 may be of well-known construction, and may consist essentially of a series of resistances corresponding in number to the number of electrical inputs (in this specific case two), connected together in parallel, the different resistance ratios being selected to convert the two input voltages to a common scale, i.e., to the same value per volt. The other electrical input sin jB'r into the summing network 21 comes from a resolver 22 of the general type shown in Fig. having as a mechanical input the quantity jB'r derived from the output of a servomechanism 23, similar to the servomechanism 14.

The two computing channels in the system of Fig. 7 feeding into the summing network 21 as described, produce the output quantity Y sin B'r-X cos B'r-sin iBr which is equal to zero according to Equation 11. However, the error voltage from the output of the summing network 21, is fed into the servomechanism 23,

which nulls this error when jB'r derived as a mechanical output satisfies Equation 11.

In Fig. 8 is shown a system, in which Equation 14 is mechanized and solved to obtain the deck tilt correction jB'r accurately. In this system, the quantities X and Y are obtained as in the system of Fig. 7, but these quantities are fed as electrical inputs into a vector solver 26 of the general type shown in Fig. 6, in conjunction with the mechanical input director train B'r derived from the gun director. The electrical outputs from this vector solver 26 are Y sin B'r-X cos B'r and Y cos Br+X sin B'r. These outputs are fed as electrical inputs into a vector solver 27 of the general type shown in Fig. 6 in conjunction with the mechanical input jB'r derived from the output of a servomechanism 28, similar to the servomechanism 14 in Fig. 7. The electrical output of this vector solver 27 is (Y sin B'r-X cos B'r) cos jB'r-(Y cos Br+X sin B'r) sin jB'r this output being equal to zero according to Equation 14. However, the error voltage from the output of this summing network, is fed into the servomechanism 28, which nulls this error when jB'r derived as a mechanical output satisfies Equation 14.

In the systems of Figs. 7 and 8, the deck tilt correction jB'r is not derived from the relative target bearing Br, so that this correction is not susceptible to perturbations in the quantity Br. Stability in director control is thereby maintained.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto, but is to be construed broadly and restricted solely by the scope of the appended claims.

What is claimed is:

1. An apparatus in a gunfire control for continuously producing a quantity corresponding to the relative target bearing Br in a form for transmittal, comprising means responsive to inputs B'r and Zd for obtaining the computed quantity sin B'r cos Zd, wherein B'r is the director train and Zd is the cross-level, means responsive to inputs B'r, Zd and L for obtaining the computed quantity cos B'r cos L--sin B'r sin Zd sin L wherein L is the level, means responsive to said computed quantities and and Br as inputs for obtaining the computed quantity sin B'r cos Zd cos Br-(cos B'r cos L-sin B'r sin Zd sin L) sin Br and a servomechanism for nulling the latter quantity to obtain the quantity Br.

2. An apparatus as described in claim 1, wherein the means for obtaining said computed quantities are electromagnetic motor-like resolver systems, each comprising a stator and a rotor with respective windings.

3. An apparatus in a gunfire control for continuously computing deck tilt correction jB'r and for continuously producing a quantity corresponding to said correction in transmittable form, comprising means responsive to inputs B'r and Zd for producing the computed quantity cos Zd sin B'r wherein Zd represents the cross-level and B'r represents the director train, means responsive to inputs B'r, Zd and L for producing the computed quantity cos B'r cos L-sin B'r sin Zd sin L, wherein L represents the level, means responsive to said computed quantities and the quantity B'r as inputs for producing the computed quantity cos B'r cos L-sin B'r sin Zd sin L) sin B'r-sin B'r cos Zd cos B'r means for algebraically adding the latter quantity to sin jB'r to produce a quantity which departs from zero by an amount constituting an error, and means for subjecting the error quantity to a null seeking operation to reduce said error to a minimum and to produce the quantity jB'r.

4. An apparatus as described in claim 3, wherein the means for obtaining said computed quantities are electromagnetic motor-like resolver systems, each comprising a stator and a rotor with respective windings.

5. An apparatus in a gunfire control for continuously computing deck tilt correction jB'r and for continuously producing a quantity corresponding to said correction in transmittable form, comprising means responsive to inputs B'r and Zd for producing the computed quantity cos Zd sin B'r, wherein Zd represents the cross-level and B'r represents the director train, means responsive to inputs B'r, Zd and L for producing the computed quantity cos B'r cos L-sin B'r sin Zd sin L, wherein L represents the level, means responsive to said computed quantities and to the quantity B'r as inputs for producing the computed quantity [(cos B'r cos L-sin B'r sin Zd sin L) sin 3' sin B'r cos Zd cos B'r] cos jB'r--[(cos B'r cos L-sin B'r sin Zd sin L) cos B'r+sin B'r cos Zd] References Cited in the file of this patent UNITED STATES PATENTS 2,486,781 Gittens Nov. 1, 1949 2,658,675 Darlington et al Nov. 10, 1953 2,715,274 James Aug. 10, 1955 2,795,379 Dowker et a1 June 11, 1957 

